Technical Abstract:
Pierce’s Disease (PD) of grapevines is caused by a gram-negative, xylem-limited bacterium Xylella fastidiosa (Xf). All Vitis vinifera-based cultivars are highly susceptible to Xf infection. However, some grape species from the southern United States such as V. arizonica, V. Shuttleworthii, and Muscadinia rotundifolia are resistant. Given that Xf is limited to xylem vessels, it has been hypothesized that chemical composition of host xylem sap could play an important role in Xf pathogenesis. In this comparative study, PD resistant (9621-67) and PD susceptible (9621-94) genotypes segregating from V. arizonica X V. rupestri breeding population were used. Xylem sap samples were collected from both genotypes with and without Xf infection using a pressure chamber. The metabolic profiles of xylem sap samples were analyzed using high performance liquid chromatography (HPLC). To further identify compounds, samples were subjected to trimethylsilyl derivatization treatments and analyzed by gas chromatography–mass spectrometry (GC-MS). About 20 peaks were tentatively identified as phenols, sugars, fatty acids, furfurals and furanosides by mass spectrometry. Principal component analysis (PCA) was conducted to categorize compounds that are correlated with resistance/susceptibility and infected/healthy states. Metabolic profiling coupled with PCA analysis in this study can facilitate identification and characterization of genotypic differences between PD resistant and susceptible grapevines in response to Xf infection.